﻿//
// System.Random.cs
//
// Authors:
//   Bob Smith (bob@thestuff.net)
//   Ben Maurer (bmaurer@users.sourceforge.net)
//   Sebastien Pouliot  <sebastien@xamarin.com>
//
// (C) 2001 Bob Smith.  http://www.thestuff.net
// (C) 2003 Ben Maurer
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
// Copyright 2013 Xamarin Inc. (http://www.xamarin.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

namespace System
{
	public class Random
	{
		private uint x;
		private uint y;
		private uint z;
		private uint c;

		public Random()
			: this(123456789)
		{
		}

		public Random(int Seed)
		{
			x = (uint)Seed;
			y = 987654321;
			z = 43219876;
			c = 6543217;
		}

		private uint JKiss()
		{
			x = 314527869 * x + 1234567;
			y ^= y << 5;
			y ^= y >> 7;
			y ^= y << 22;
			ulong t = ((ulong)4294584393 * z + c);
			c = (uint)(t >> 32);
			z = (uint)t;
			return (x + y + z);
		}

		public virtual int Next(int minValue, int maxValue)
		{
			if (minValue > maxValue)
				throw new ArgumentOutOfRangeException("Maximum value is less than minimal value.");

			// special case: a difference of one (or less) will always return the minimum
			// e.g. -1,-1 or -1,0 will always return -1
			uint diff = (uint)(maxValue - minValue);
			if (diff <= 1)
				return minValue;

			return minValue + ((int)(JKiss() % diff));
		}

		public virtual int Next(int maxValue)
		{
			if (maxValue < 0)
				throw new ArgumentOutOfRangeException("Maximum value is less than minimal value.");

			return maxValue > 0 ? (int)(JKiss() % maxValue) : 0;
		}

		public virtual int Next()
		{
			// returns a non-negative, [0 - Int32.MacValue], random number
			// but we want to avoid calls to Math.Abs (call cost and branching cost it requires)
			// and the fact it would throw for Int32.MinValue (so roughly 1 time out of 2^32)
			int random = (int)JKiss();
			while (random == int.MinValue)
				random = (int)JKiss();
			int mask = random >> 31;
			random ^= mask;
			return random + (mask & 1);
		}

		public virtual void NextBytes(byte[] buffer)
		{
			if (buffer == null)
				throw new ArgumentNullException("buffer");

			// each random `int` can fill 4 bytes
			int p = 0;
			uint random;
			for (int i = 0; i < (buffer.Length >> 2); i++)
			{
				random = JKiss();
				buffer[p++] = (byte)(random >> 24);
				buffer[p++] = (byte)(random >> 16);
				buffer[p++] = (byte)(random >> 8);
				buffer[p++] = (byte)random;
			}
			if (p == buffer.Length)
				return;

			// complete the array
			random = JKiss();
			while (p < buffer.Length)
			{
				buffer[p++] = (byte)random;
				random >>= 8;
			}
		}

		public virtual double NextDouble()
		{
			// return a double value between [0,1]
			return Sample();
		}

		protected virtual double Sample()
		{
			// a single 32 bits random value is not enough to create a random double value
			uint a = JKiss() >> 6;  // Upper 26 bits
			uint b = JKiss() >> 5;  // Upper 27 bits
			return (a * 134217728.0 + b) / 9007199254740992.0;
		}
	}
}
